Method and composition for producing a black matte finish on ferrous metals

ABSTRACT

A method is provided for producing a black matte finish on ferrous metal objects, wherein the ferrous metal object is contacted with a sulfuric acid solution of a trivalent antimony salt and a complexing agent and thereafter a phosphate coating is deposited on the object. The treating solution may also contain a minor amount of hydrochloric acid or a salt of hydrochloric acid. The finish produced on the ferrous metal is of a uniform black stable shade.

United States Patent Schlossberg et al.

[54] METHOD AND COMPOSITION FOR PRODUCING A BLACK MATTE FINISH ONFERROUS METALS [72] Inventors: Louis Schlossberg, Farmington; Stanley M.

Sokalski, Southfield, both of Mich.

[731 Assignee: Detrex Chemical Industries, Inc., Detroit,

Mich.

[221 Filed: Oct. 21, 1969 21 Appl. No.: 868,218

[52] US. Cl. ..148/6.15 R, 148/6.15 Z, 148/315 [51] Int. Cl..... C23f7/10 [58] Field ofSearch ..l48/6.l7,6.14, 6.15 R,3I.5

[56] References Cited UNITED STATES PATENTS 1,436,729 11/1922 Scanlan..148/6.14

[ 5] Feb. 22, 1972 2,271,706 2/1942 Morris ..1 17/70 3,372,064 3/1968Jones et al. ..148/6.l4 X

OTHER PUBLICATIONS Hopkins, The Scientific American Cyclopedia ofFormulas 1925 Scientific American Pub. Co. pp. 444, 448.

Primary Examiner-Ralph S. Kendall AttomeyPau1 & Paul [57] ABSTRACT 8Claims, No Drawings METHOD AND COMPOSITION FOR PRODUCING A BLACK MATTEFINISH ON FERROUS METALS BACKGROUND OF THE INVENTION 1. Field of theInvention This invenfion relates to a process for treating ferrousmetals. More particularly this invention is concerned with a method forproducing a black matte finish on ferrous metals.

2. Description of the Prior Art Black matte finishes are required oncertain ferrous metal products. Depending on the particular methodemployed to form the black matte finish, the finish can be decorative,protective, or used as a bonding layer for additional treatments such asphosphate coating treatments. Various methods have been suggested in theprior art to form a black matte finish on ferrous metals. None of themethods suggested to date have proven to be completely satisfactory.Certain of the methods employed have produced somewhat uneven results,and the shade of black was not sufficiently deep.

The most commonly employed method suggested in the prior art utilizesthe compounds of arsenic, antimony, tin or nickel to obtain the desiredfinish. However, the disclosed processes generally required specialreaction conditions which limited their use in the large scaletreatments of ferrous metals, or substantially increased the cost of thetreatment. One method consisted of treating the metal with a hydrocarbonsolution, for example a kerosene solution of the antimony salts (ArentU.S. Pat. No. 1,770,828). It can be seen that this method was notsatisfactory because of the substantial fire hazard and the problem ofremoving the solvent from the treated metal. Other methods suggested inthe prior art consisted of treating the metals with alkaline solutionscontaining reactants such as an antimony compound (Scanlan U.S. Pat.

Certain of the methods suggested in the prior art were conducted in anacid media. However, the particular acids which could be employed wererather limited. It was indicated in the prior art (Morris U.S. Pat. No.2,271,706, Jones U.S. Pat. No. 3,372,064) that hydrochloric acidsolution of trivalent antimony salts could be employed. These referencesspecifically taught against using acids such as sulfuric or nitric acid.It was recognized in the prior art that the trivalent antimony salts arereadily oxidized to the pentavalent state by the sulfuric acid, andaccordingly sulfuric acid was excluded from the treatment baths. Theprocesses using the relatively concentrated hydrochloric acid solutionswere not completely satisfactory. Because of the relatively highconcentrations of acid required, there was considerable amounts ofhydrochloric acid fumes in the area adjacent the treating equipment. Inaddition, the concentrated hydrochloric acid solutions were highlycorrosive causing considerable damage to the processing and ventilationequipment.

A further difficulty in employing the prior art process for applyingblack matte finishes was that ferrous metals are often pretreated bypickling them in sulfuric acid. Once any residual sulfuric acid was lefton the pickled ferrous metals, it would cause oxidation of the treatingbaths.

1! is the object of the invention to provide a method of obtaining blackmatte finishes on ferrous metals which are a deep and uniform shade.

It is a further object of this invention to provide a method wherein themetal may be treated under acid conditions.

It is still a further object of the invention to provide an improvedprocess for the production of black matte finish on ferrous metals whichcan be conducted in a continuous manner with a minimal amount ofcontrols in the presence of sulphuric acid andwhich will produce uniformresults.

Other objects and advantages of the present invention will becomefurther apparent from a reading of the specifications, examples andsubjoined claims.

. 2 SUMMARY OF THE INVENTION The object ofthis invention has beenachieved by providing a method wherein a black matte finish is formed onferrous metals by treating the metals with an aqueous sulfuric acidsolution containing a trivalent antimony salt and a complexing agentandthereafter depositing a phosphate coating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Aqueous solution which consistsof only sulfuric acid and a trivalent antimony salt such as antimonytrichloride are unsuitable for forming black matte finishes on ferrousmetals in that the sulfuric acid in the solution oxidizes the trivalentantimony to the pentavalent state. It was for the above reasons that theprior art specifically taught against the use of sulfuric acid. However,it has been found that sulfuric acid solutions of trivalent antimonycompounds can be used effectively and excellent results obtained onferrous metals if, in addition to the sulfuric acid and the trivalentsalt, a complexing agent is added to the treating bath. The exact effectof the complexing agent on the treating solution is not known. Ferrousmetals treated with the sulfuric acid solution containing a complexin gagent and a trivalent antimony salt and thereafter treated with aphosphate coating have a deep level, stable, matte finish.

The compositions used in the present invention advantageously containfrom about 9 grams per liter to about 235 grams per liter of sulfuricacid (calculated at percent concentration). Amounts less than 9 gramsper liter can be employed but the reaction time is considerablyincreased so that it becomes impractical to use amounts substantiallyless than 9 grams per liter. It is also possible to use a higherconcentration of sulfuric acid, however the higher concentrations aresomewhat impractical for most commercial installations.

The trivalent salts employed in the present invention may be any of thewater soluble salts of trivalent antimony with the preferred trivalentantimony compound being antimony trichloride.

Since the antimony ion is the effective reactant of the treatingcomposition with regard to the formation of the black coating on theferrous metal, it is of advantage to have a maximum amount of thetrivalent antimony salt in the treating solution. Accordingly, the upperlimit of the amount of the trivalent antimony salt in the treatingcomposition is governed by the solubility of the salt in the treatingcomposition. There is no lower limit with regard to the amount of thetrivalent antimony salt which can be added to the composition. However,for practical purposes there must be a minimal amount of the trivalentantimony salt in the composition in order to obtain the desired effectin a reasonable length of time. Using antimony salt, the amount of theantimony trichloride which is preferably employed is between 0.5 gramper liter to about 15 grams per liter.

Various types of well known complexing agents can be employed in thepresent invention. Compounds which deserve particular attention in thisregard are, for example, tartaric acid, gluconic acid, citric acid,glycolic acid, phytic acid, kojic acid, sorbitol andethylenediamine-tetraacetic acid, with tartaric acid being the preferredcomplexing agent for employment in the present invention. The amount ofthe complexing agent that is added to the composition of this invention,is dependent on the particular complexing agent which is employed andthe relative amount of sulfuric acid and the trivalent antimony salt inthe composition. The amount of a particular complexing agent which mustbe added in order to be effective in preventing the oxidation of thetrivalent antimony to the pentavalent state in a given composition canreadily be determined on a small scale by preparing compositionscontaining various amounts of the complexing agent and the requiredamount of sulfuric acid and the trivalent antimony, and increasing theamount of the complexing agent in each composition until a stablecomposition is obtained.

Using tartaric acid as an example, an amount at least 0.5 gram perliteris required in order to have a stable solution.

However, amounts in excess of this are generally employed with theamount up to 20 grams per liter being practical. Amounts above 20 gramsper liter are generally not employed in that the excess amounts do nothave any beneficial effect on the stability of the solution.

When the surfaces of the ferrous metalswhich are to be treated aresomewhat contaminated, as for example by having a light oxide filmcoating or a film of a lubricant thereon, it is considerablyadvantageous to include in the treating composition a small amount ofeither hydrochloric acid or a salt of hydrochloric acid. The amount ofhydrochloric acid that is employed can be relatively small, with at most10 grams per liter of hydrochloric acid calculated on 100 percentconcentration being required. Generally however, amounts between 1 and10 grams per liter are quite sufficient to remove any contamination fromthe surface of the metals to be treated. Various types of hydrochloricacid salts can be used. These would include the acid salts and even theneutral salts such as sodium chloride. The amount of the salt that isadded is calculated so that the chloride ion concentration would beequivalent to that when l-10 grams of hydrochloric acid calculated at100 percent concentration is used.

In accordance with the method of this invention, the ferrous metalobject on which the black matte coating is to be formed is thoroughlycleaned. The metal object is contacted with the sulfuric acid solutionof the trivalent antimony salt and the complexing agent. The object maybe immersed in a bath of the composition or the composition may besprayed onto the subject. The object should be in contact with thetreating solution for between 0.5 and minutes with the treating solutionat a temperature from 60 to 100 F. Higher treating temperatures andlonger treating times can be employed to increase the thickness of theblack matte coating on the treated object. Depending upon the surfaceinvolved, a small quantity of HCl may be added to the pretreat solutionin quantities up to about g./. Following treatment with the sulfuricacid solution, the metal object is rinsed with water. The object, as aresult of this treatment has a black coating on the surface thereof.

The treated object is thereafter subjected to a phosphate coatingtreatment. The composition of the phosphate coating bath is notcritical. Any of the well-known phosphate compositions may be employed.In addition to the zinc and phosphate ions, it is of advantage toinclude nickel ions. 7

Especially good results are obtained with the process of the presentinvention when phosphate solutions such as those disclosed inSchlossberg et al. U.S. Pat. No. 3,269,877 are employed. These phosphatecompositions impart an additional blackening effect, in addition tosubstantially improving the physical properties of the black mattefinish.

The following examples are given by way of illustration of additionalcompositions included within the scope of the present invention and arenot intended to limit in any way the scope of the subjoined claims. Allpercentages are percent by weight unless otherwise indicated.

EXAMPLE 1 A cleaned and pickled 4X4 inch cold rolled steel test panelwas immersed for 1 minute at 80 F. in an aqueous solution containing 88grams per liter of sulfuric acid, (calculated at 100 percentconcentration), 2 grams per liter of antimony trichloride, and 2 gramsper liter of tartaric acid. The test panel was rinsed in cold water. Thetest panel at this stage had a black coating deposited on its surface. Aphosphate coating was deposited on the surface by immersing the testpanel in an aqueous solution containing 0.9 percent phosphate ion (H PO0.28 percent nitrate ion (HNO 0.351 percent zinc ion (ZnO) and 0.012percent cobalt ion (Co(NO The sample was immersed for minutes at atemperature between l90-200 F. The panel was rinsed with hot water anddried.

The test panel after this treatment had a uniform black matte finish.

EXAMPLE 2 Example 1 was repeated with the exception that the test panelwas not pickled and which had a slight but visual oxide coating. Thetreated test panel had an uneven black matte finish.

EXAMPLE 3 Example 1 was repeated with the exception that a test panel ofcold rolled steel having a slight but visual oxide coating was employedand 10 grams per liter of hydrochloric acid (calculated at percentconcentration) was added to the treating composition. The treated sampleafter the phosphate treatment had a uniform black matte finishequivalent to the finish on the test panel prepared in Example 1.

EXAMPLE 4 Test panels of cleaned and pickled cold rolled steel wereimmersed in an aqueous treating composition comprised of 100 grams perliter of sulfuric acid (calculated at 100 percent concentration), 10grams per liter of antimony trichloride (anhydrous) and 10 grams perliter of tartaric acid, for the times and temperatures noted below, andthereafter a phosphate coating was applied as described in Example 1.

Example 1 was repeated with the exception that 12 grams per liter ofgluconic acid was employed in place of the tartaric acid. The resultsobtained were equivalent to the results obtained in Example 1 EXAMPLE 6Example 1 was repeated with the exception that 12 grams per liter ofcitric acid was employed in place of the tartaric acid. The black mattefinishes obtained on the samples in this example were equivalent tothose in Example 1.

EXAMPLE 7 Example 1 was repeated with the exception that the tartaricacid was replaced with 1 gram per liter of glycolic acid. The resultsobtained in this example were equivalent to the results obtained inExample 1.

EXAMPLE 8 Example 1 was repeated with the exception that the tartaricacid was replaced with 8 grams per liter of phytic acid. The coatingobtained in this example was equivalent to the coating obtained inExample 1.

EXAMPLE 9 Example 1 was repeated with the exception that the tartaricacid was replaced with 6 grams per liter of kojic acid. The coatingobtained in this example was the same as the coating obtained in Example1.

EXAMPLE 10 Example 1 was repeated with the exception that the tartaricacid was replaced with 9 grams per liter of sorbitol. The sampicstreated in accordance with this example were equivalent to the samplesobtained in Example 1.

EXAMPLE 11 Example 1 was repeated with the exception that the tartaricacid was replaced with 5 grams per liter of ethylenediaminetetraaceticacid. Samples treated in accordance with this example were equivalent tothe samples obtained in Example 1.

EXAMPLE l2 Measured test panels of cold rolled steel were treated atroom temperature (70 F.) for one minute with the aqueous compositioncomprised of 88 grams per liter of sulfuric acid (calculated at 100percent), 2 grams per liter of antimony trichloride (anhydrous) and 2grams per liter of tartaric acid (anhydrous) and grams per liter ofhydrochloric acid (calculated at 100 percent) and thereafter a phosphatecoating was applied as in Example 1.

The treated samples had a uniform black matte finish. It was found thatwhen the above solution was employed as the finishing agent forobtaining the black matte finish, that it could satisfactorily treat 140sq. feet of the steel panels per gallon of treating solution beforeserious depletion of the solution occurs.

EXAMPLE 13 Example 1 was repeated with the exception that the phosphatecoating solution employed in Example 1 was replaced with a phosphatesolution comprised of 0.9 percent phosphate ion (H Po 0.284 percentnitrate ion (HNO and 0.35 1 percent zinc ion (ZnO). The test panel had adeep black matte finish which was slightly lighter in color than thesample prepared in Example 1 but it would be of desirable andcommercially acceptable quality.

We claim:

1. The method of forming a black matte finish on a ferrous metal objectwhich comprises contacting said object with an aqueous solutioncomprised of: about 9-235 grams per liter of sulphuric acid; an amountof a water soluble trivalent antimony salt up to the limit of solubilityof said salt in said solution and an effective amount of complexingagent selected from a group consisting of tartaric acid, gluconic acid,citric acid, glycolic acid, phytic acid, kojic acid, sorbitol, andethylenediaminetetraacetic acid, said effective amount being an amountsufficient to prevent oxidation of said trivalent antimony salt in saidsolution to the pentavalent state; said object being contacted with saidsolution from about 0.5 to about 5 minutes at a temperature of about 60F. to about F., and thereafter depositing a phosphate conversion coatingon said object.

2,. The method according to claim 1, wherein said trivalent antimonysalt is antimony trichloride.

3. The method according to claim 1, wherein said complexing agent istartaric acid.

4. The method according to claim 1 wherein said solution furthercontains a member selected from the group consisting of hydrochloricacid or a salt of hydrochloric acid.

5. The method according to claim 1 wherein said solution contains up to10 grams per liter of hydrochloric acid.

6. The method according to claim 1 wherein said aqueous solution iscomprised of from about 9 to 235 grams per liter of sulfuric acid, 0.5to 15 grams per liter of antimony trichloride, 0.5 to 20 grams per literof tartaric acid, and 0 to 10 grams per liter of hydrochloric acid, andsaid object is contacted for 0.5 to 5 minutes at room temperature to 100F. with said solution.

7. The aqueous solution for employment in the method according to claim1 comprised of about 9 to about 235 grams per liter of sulfuric acid,0.5 to 15 grams per liter of a trivalent antimony salt, 0 to 10 gramsper liter of hydrochloric acid and an effective amount of a complexingagent.

8. The ferrous metal ob ect having a black matte finish appliedaccording to the process of claim 1.

2. The method according to claim 1, wherein said trivalent antimony saltis antimony trichloride.
 3. The method according to claim 1, whereinsaid compLexing agent is tartaric acid.
 4. The method according to claim1 wherein said solution further contains a member selected from thegroup consisting of hydrochloric acid or a salt of hydrochloric acid. 5.The method according to claim 1 wherein said solution contains up to 10grams per liter of hydrochloric acid.
 6. The method according to claim 1wherein said aqueous solution is comprised of from about 9 to 235 gramsper liter of sulfuric acid, 0.5 to 15 grams per liter of antimonytrichloride, 0.5 to 20 grams per liter of tartaric acid, and 0 to 10grams per liter of hydrochloric acid, and said object is contacted for0.5 to 5 minutes at room temperature to 100* F. with said solution. 7.The aqueous solution for employment in the method according to claim 1comprised of about 9 to about 235 grams per liter of sulfuric acid, 0.5to 15 grams per liter of a trivalent antimony salt, 0 to 10 grams perliter of hydrochloric acid and an effective amount of a complexingagent.
 8. The ferrous metal object having a black matte finish appliedaccording to the process of claim 1.